1. Field of the Invention
The present application relates to a conductive layer and a method of manufacturing the same.
2. Discussion of Related Art
Various apparatuses such as a liquid crystal display (LCD), a light emitting diode, and a solar cell need a conductive layer having high transparency to visible light and low resistance.
Recently, according to propagation of mobile devices and demands for smaller and lighter devices, it is required that the conductive layer be formed on a lighter substrate.
While the most frequently used transparent conductive layer is a transparent conducive layer (so called, an indium tin oxide (ITO) layer) having indium-tin-oxygen (In—Sn—O) formed on a glass substrate as a main component, due to the recent demands for the smaller and lighter devices, it is also considered that a conductive layer be formed on a plastic base layer, which is lighter than the glass substrate.
A conductive layer is usually formed by DC magnetron sputtering, RF magnetron sputtering, vacuum deposition, or ion plating. However, the conductive layer formed on a plastic base layer by the above-described method, for example, an ITO layer, generally has a lower resistance characteristic than an ITO layer formed on a glass substrate.
There are many reasons for the lower resistance, but a representative one may be that the plastic base layer has a lower thermal resistance than the glass substrate. That is, because of deterioration of the thermal resistance, the ITO layer should be formed at a lower temperature than that of the glass substrate, and thus crystals of the ITO layer cannot be sufficiently grown.
Crystallinity of the ITO layer may be determined by X-ray diffraction (XRD). For example, according to the XRD analysis, in a polycrystalline ITO layer, three reflections are observed. An index of the reflections is determined by a mirror index, and these reflections are derived from (222), (400) and (440) planes from a lower angle side. When Cu-kα is used as an X-ray source, it is known that reflection from the (222) plane is shown at approximately 30.5 (2θ) degrees, reflection from the (400) plane is shown at approximately 35 (2θ) degrees, and reflection from the (440) plane is shown at approximately 50.5 (2θ) degrees. For example, in FIG. 4 of Non-patent reference 1 [┌Transparent conductive film┘ (┌HYOUMEN┘ vol. 18, No. 8 (1980) 440-449)], an XRD pattern of a thermally treated crystalline ITO layer deposited a polyester film is disclosed. In addition, in Non-patent reference 2 [┌SHINKU┘ vol. 30, No. 6, 546-554], an XRD pattern of the crystalline ITO layer formed on a glass substrate by sputtering is disclosed. On an XRD intensity curve, peaks derived from the reflection from the (222), (400) and (440) planes were shown.
It is known that conventional structure and characteristics of the ITO layer are highly dependent on a temperature of forming the ITO layer. The ITO layer formed at low temperature such as room temperature is usually amorphous.
For example, a method of controlling crystal alignment for the (400) plane to be parallel to a glass substrate to reduce a resistance of the ITO layer formed on the substrate is suggested in Japanese Patent Application Laid-Open No. 1995-090550. In Japanese Patent Application Laid-Open No. 1995-090550, the ITO layer formed in a direction 100, for example, formed such that the (400) plane is parallel to the substrate, decreases in resistivity. To realize the crystal alignment, it is important to form the ITO layer at a high temperature of 200° C. or more.
There are several researches to control crystal alignment in a high temperature process for forming a layer at high temperature.
It is known that a structure of the ITO layer formed on the glass structure varies depending on a forming atmosphere. For example, in Japanese Patent Application Laid-Open No. 1997-050712, the diameter and number of a crystal may be controlled in an atmosphere in which vapor, which is an impurity gas, is present, and in Japanese Patent Application Laid-Open No. 1996-092740, a method of controlling a structure of a layer by actively removing an impurity gas and building a vacuum system is disclosed.
However, since the plastic base layer may not be usually heated at high temperature, crystals may not be sufficiently grown during the formation of the conductive layer, and it is difficult to realize physical properties such as a low resistance like a glass substrate.